Carbon molecular sieves produced from walnut shell

Abstract

Recently, the development of carbon molecular sieves (CMS) for the separation of various gases, particularly air into oxygen and nitrogen, has gained widespread attention. In this paper, a simple method was presented for preparing carbon molecular sieves. Carbonized walnut shells were impregnated with a small amount of potassium hydroxide (KOH) and pyrolysed. In this way, the pore size can be easily controlled in the range around 0.5 nm. The produced samples were further modified by a carbon deposition to form the final CMS. 3-methylpentane (3-MP) was used as a carbon source for the deposition. The CMS samples were characterized by the adsorption of nitrogen, oxygen, and a series of molecular probes to estimate the surface area, pore volume, and the pore size distributions. Due to the small pore entrances, only a very small nitrogen adsorption was found on the CMS at 77 K. Therefore, the oxygen adsorption isotherms at 77 K were used to calculate the surface area and pore volume. We are able to prepare CMS with a narrow pore size distribution in the range 0.33–0.43 nm and with an oxygen-to-nitrogen separation selectivity, D O 2 D N 2 , as high as 9.2.